$5-7.$ A refrigerator runs on the vapor$-$compression cycle. The boiler operates at $T=265K$ and the condenser operates at $305K.$ The compressor has an efficiency of $85\%.$ Thermodynamic data for two different refrigerants is located in Appendix F$.$

A$.$ What is the maximum attainable coefficient of performance for Freon ${?}^{}22?$

B$.$ What is the maximum attainable coefficient of performance for refrigerant HFC$-134$a$?$

C$.$ Besides coefficient of performance, two considerations in choosing a refrigerant are price and safety. Research Freon ${?}^{}22$ and HFC$-134$a and comment on their suitability as refrigerants.